Obviously they don’t take The Bible seriously.
The Torah includes specific regulations on the practice of polygamy, such as Exodus 21:10, “If he takes another wife to himself, he shall not diminish her food, her clothing, or her marital rights.” Deuteronomy 21:15–17, says that a man must award the inheritance due to a first-born son to the son who was actually born first, even if he hates that son’s mother and likes another wife more and Deuteronomy 17:17 states that the king shall not have too many wives.[3]
The first polygamist mentioned in the Bible is Lamech, whose two wives were Adah and Zillah (Genesis 4:19). Many important figures had more than one wife, such as Esau (Genesis 26:34; Genesis 28:6-9), Abraham (Genesis 16:3, Genesis 21:1-13, Genesis 25:1, Genesis 25:6), Moses (Exodus 2:21; Exodus 18:1-6, Numbers 12:1), Jacob (Genesis 29:15-28), Gideon (Judges 8:29-32), Elkanah (1 Samuel 1:1-8), David (1 Samuel 25:39-44; 2 Samuel 3:2-5; 2 Samuel 5:13-16) and Solomon (1 Kings 11:1-3).